Chronoaging results in general degradation of the skin. Wrinkling and thickening of the skin induced by solar light result in sagging, reduced elasticity of skin, dry skin and mottling, and other harmful effects are additively increased by exposure to sunlight and this phenomenon is called “photoaging”. Deterioration of the epidermis and dermis, wrinkling, yellowing, thickening and reduced elasticity of skin are all associated with photoaging.
To solve this problem, uses of retinoid (vitamin A) have been reported in U.S. Pat. Nos. 4,603,146 and 4,877,805. There are Retinol (Vitamin A alcohol), Retinal (Vitamin A aldehyde), Retinyl acetate, Retinyl propionate, Retinyl linoleate and Retinyl palmitate in the Retinoid group. Among elements of retinoid group, retinol is a compound which can be naturally found in the human body and is essential in the specialization and growth of epithelium. Moreover, retinol is superior to other retinoids (such as retinoic acid) in terms of safety for living creatures, so retinol is suitable for skin-care cosmetic material. In case of excessive intake, retinol is chiefly stored as an inactive form of retinyl palmitate, and a small quantity is stored as an inactive form of retinyl acetate in the human body.
Skin care compositions containing retinoids have become quite prominent in recent years and particularly retinol, also known as Vitamin A, is well known as a treatment for acne, so many medical or pharmaceutical goods containing retinol, including types of ointments are produced and consumed. Even more recently, many other benefits of retinol have been revealed, and the typical examples are effects against photoaging and sun-damage.
In spite of these beneficial effects, retinal is easily oxidized and denatured, and loses its characteristic color, odor when contacting with air, oxygen, heat or aqueous solution, so original potency is lowered significantly. Also, pure retinal induces skin irritation even when used in small amounts. Due to these drawbacks, retinal has been limitedly incorporated into cosmetic formulations.
Many studies have been conducted to stabilize retinal in a cosmetic composition. U.S. Pat. No. 08-769130 reports a double-encapsulation method which comprises the steps of (a)first-encapsulating the retinal with filming materials such as glycosaminoglycan to give a microcapsule; and (b) encapsulating the microcapsule of the step (a) with gellan gums. This technique stabilizes doubly retinal, however the second-encapsulating with gellan gums is a kind of an open matrix system, therefore this method is limitedly effective in protecting retinal from oxygen, air or heat.
There has also been proposed an oil-in-water type (O/W type) emulsion wherein retinoic acid is stabilized with a fat-soluble antioxidant such as BHT (butylated hydroxytoluene) and dl-a-tocopherol or a chelating agent such as EDTA in U.S. Pat. No. 3,906,108. U.S. Pat. No. 4,247,547 reports an oil-in-water type (O/W type) emulsion wherein fat-soluble active material is stabilized with a fat-soluble antioxidant consisting of tocopherol, citric acid.
U.S. Pat. No. 4,826,828 reports a water-in-oil type (W/O type) emulsion wherein retinol, retinyl acetate and retinyl palmitate are stabilized by an antioxidant such as BHT (butylated hydroxytoluene), or BHA (butylated hydroxyanisole). U.S. Pat. No. 4,720,353 reports a water-in-oil type (W/O type) emulsion wherein retinol is stabilized with an antioxidant such as BHA (butylated hydroxyanisole), ascorbic acid or tocopherol.
E.P. 0440398 (B1) reports an oil-in-water type (O/W type) emulsion wherein retinol is stabilized with one or more kinds of water-soluble antioxidants or chelating agents to improve chemical stability of retinol. A European Patent application also reports an oil-in-water type (O/W type) emulsion wherein retinol is stabilized with a chelating agent, water, fat-soluble antioxidants and free-base type imidazole.
As stated above, most patents refer to stabilizing methods wherein antioxidants and chelating agents are the prime elements. However the only difference between patent techniques is the kind of chelating agents and properties of antioxidants used, so with these methods, retinol cannot be protected from oxygen, moisture or heat effectively.